To form composites of inorganic particles such as silica, alumina, titania and zirconia in organic polymers has been widely studied for providing both properties of organic polymers such as formability and flexibility and those of inorganic compound such as heat resistance, wear resistance, and surface hardness. To achieve a sufficient effect to form composites by this method, it is preferable that inorganic particle having small a size as possible be formed in the composite at a high content. The smaller the particle size of the inorganic particles, the larger the surface area per weight of the inorganic particles becomes and the wider the interface region between the organic material and the inorganic particles becomes, thereby a high reinforcement effect can be expected (area effect). The higher the inorganic particle content, the greater is the characteristic of the composite in all reason (volume effect). However, when inorganic particles having a small size and contained at a high content are used to form a composite with the organic polymer, there were problems that the dispersibility of the inorganic particles in the organic polymer becomes low, the agglomerating property increases and the objective properties cannot be obtained.
The inorganic particles inherently differ from the organic polymer in terms of surface properties, specific gravity, heat-stability, and insolubility to chemicals, thereby it is extremely difficult to produce a uniform and fine dispersion when using a high content of inorganic particles. Additionally, inorganic particles of nanometer order are expensive generally and handling thereof is difficult due to the possibility of scattering. When trying to forcibly mix the inorganic particles with the organic matrix using large-scale dispersion equipment such as an extruder, a large quantity of thermal energy is needed (for example, see patent document 1). In example 1 of patent document 1, a melt blending treatment is accomplished at 200° C.
On the other hand, using a so-called sol-gel method in which a metal alkoxide is subjected to a hydrolysis polycondensation reaction to become a metal oxide, to form a composite of a nanometer order metal oxide with the organic polymer has been extensively studied (for example, see patent documents 2 and 3). By this method, a uniform and fine dispersion of the metal oxide in the organic polymer is easy to achieve and this method has an advantage in the mean energy utilized since the polycondensation reaction occurs at a rather low temperature from around ordinary temperature to 150° C. However, there is a problem in that the production efficiency is extremely low since both the hydrolysis and polycondensation reactions need a long time. In Example 1 of patent document 2, after 48 hours of stirring treatment at room temperature to achieve hydrolysis, a further 21 hours are needed at around 100° C. for polycondensation. In a similar way in patent document 3, one day at room temperature and one more day at 80° C. are needed for each reaction.
To gain an organic-inorganic composite material by the sol-gel method, a metal alkoxide which can cause the sol-gel reaction is required. Therefore, it is impossible to form a composite using metal species which do not form a metal alkoxide. Metal alkoxides are generally expensive materials and composites thereof become expensive to produce.
A production method of a composite of polyamide and glass is known (for example, see patent document 4). The invention described in patent document 4 produces a composite of glass and polyamide easily using inexpensive water glass by putting (A) an aqueous solution phase including water, water glass and diamine monomer into contact with (B) an organic solution phase including organic solvents and acylated dicarboxylic acid monomer, and reacting the monomers by a polycondensation reaction at the boundary face of both solution phases. However, the properties provided to the composite are limited to thermal and mechanical stability and other properties cannot be provided since only glass as an inorganic composition can be introduced to the polyamide by the invention.
Patent document 1    Japanese Unexamined Patent Application, First Publication No. Hei6-279615
Patent document 2    Japanese Unexamined Patent Application, First Publication No. Hei8-157735
Patent document 3    Japanese Unexamined Patent Application, First Publication No. Hei8-319362
Patent document 4    Japanese Unexamined Patent Application, First Publication No. Hei10-176106